As is well known in the art, contemporary practice typically employs a power supply control apparatus for a computer system having three portions, that is a main body, a display apparatus and cable lines that are used for transmission of a display signal including a video signal and a synchronizing signal and for establishing electrical conduction path between the main body and display apparatus. Another exemplar of a power supply apparatus of a computer system provides for a display apparatus that is not powered directly from an external power source, but rather from a power supply in main body portion of a computer system.
As previously noted, conventional power supply circuit is designed to save power consumption required for a proper operation of various circuits to some extent when power consumption is shifted to a power saving mode under the control of display power management system (DPMS). It is observed however that even in a power saving mode, constant level of power consumption is still kept so as to continuously support a heater operation and to supplement a leakage current. This is an inherent drawback to the above described power supply circuit.
In addition, repeated switching operation of a power supply switching device in normal conditions can cause wear and tear as well as contact noise. Such drawbacks as described cause product efficiency to drop in a mass production environment, increasing overall production of a display apparatus Further, the manufacturers must undertake the inconvenience of additional manufacturing steps to produce a manually operated power supply switching device. Additionally, an additional switching device may detract aesthetic visual appearance from a display apparatus.
Earlier monitor driving devices include a power supply source for supplying power to a computer, a computer circuit operated by the power supply source for outputting a video control signal for operating a corresponding device, and a monitor operated in response to the video control signal from the computer circuit. The power supply source includes a computer power supply for supplying the power to the computer circuit and a monitor power supply for supplying power to the monitor in response to a monitor power control signal on the computer circuit.
The monitor includes a monitor circuit operated in response to the power supply from the monitor power supply and the video control signal from the computer circuit, a cathode ray tube (CRT) receiving the power from the monitor power supply and operated in response to a cathode ray tube control signal from the monitor circuit. When power is supplied to the power supply, the monitor power supply supplies the power to the monitor circuit and the cathode ray tube. The computer power supply supplies the power for operating the computer circuit. When a video control signal is input to the monitor circuit from the computer circuit, the monitor circuit outputs a cathode ray tube control signal to the cathode ray tube and is operated in the video image signal corresponding to the video control signal from the computer circuit.
In the earlier designs for a monitor driving device, the power consumption by the monitor can be reduced by the monitor power control signal from the computer circuit. The computer circuit outputs a monitor power control signal at a low level to the monitor power supply to reduce the power consumption by the monitor. The monitor power supply cuts off the power to the monitor circuit and the CRT, thereby reducing the power consumption while the monitor is not being used. The monitor control signal at high level is from the computer circuit to the monitor power supply to use the monitor again by operating the monitor circuit and the cathode ray tube in which the power was previously cut off. I have found however, the earlier monitor driving device has a disadvantage in that it takes too much time to display an image on the screen of the cathode ray tube due to the heating time of the cathode ray tube when the monitor driving device is turned off by the monitor power control signal and again turned on by the monitor power control signal at the high level after passing a predetermined time. I have also noticed that the earlier monitor driving device has another disadvantage in that the life span of the cathode ray tube is reduced when the voltage is continuously applied to the cathode ray tube to preheat the cathode ray tube.
Recent efforts in the art such as the patent to Song, U.S. Pat. No. 5,483,464, entitled Power Saving Apparatus For Use In Peripheral Equipment Of A Computer, is but one example of an apparatus for turning off peripheral equipment (such as a monitor) in a computer apparatus to save power in a stand-by state. Walker patent, U.S. Pat. No. 5,335,168 entitled Computer System With Power-Down Mode For Monitor, endeavours to conserve power by powering down the monitor much in the fashion noted above. In addition, a diode is utilized to supply a voltage lower than normal voltage to the filament 40 of the cathode ray tube to decrease the period of the time needed for the cathode ray tube to again be operated after being in a stand-by state. I have observed that the efforts in the art represented by Walker '168 however, seem to lack the ability to directly supply the power for the lower voltage generated from the computer power supply. Such an interval for warming up a heater may even deteriorate an image representation on the screen of a cathode ray tube (CRT).
In a typical exemplar of contemporary practice for supplying power to a monitor associated with a computer system, a power supply circuit includes a rectifier for rectifying supplied alternating current power and for generating a rectified direct current source voltage, a first power generator for receiving a direct current from the rectifier and for generating power in a switching mode power supply SMPS mode, a first power supply supplied with power from the first power generator for supplying power to various circuits in a monitor, a second power generator fed with direct current from the rectifier for generating power in a switching mode power supply mode, and a second power supply supplied with power from the second power generator for generating power for use by a computer system. The rectifier is supplied from a commercially available external power source with alternating current AC (110 Volts/220 Volts), rectifying and smoothing the supplied power by using a combination of a diode and capacitor, generating rectified power at a constant voltage level of direct current. The first power generator is supplied with a direct current and generates power in a switching mode power supply SMPS mode. The first power supply is supplied with power from the first power generator and supplies power at different voltage levels so as to energize various circuits in a monitor. The second power generator is supplied with direct current from the rectifier and generates power in a switching mode power supply mode. The second power supply is supplied with power from second power generator and supplies power at different voltage levels so as to energize various circuits in a computer system. When an operation of a computer system is suspended for a predetermined time interval, the first power generator supplies no power to the first power supply upon receiving a power saving signal output from a microcomputer (not shown). A switching mode power supply SMPS mode is well known in the art so that no further explanation will be provided. Upon observation of contemporary art as previously described, there is found drawbacks as mentioned above.